1. Field of the Invention
This invention relates to circular knitting machines and in particular to the selection of needles in such machines for the purpose of producing patterned knitwork, and provides a device and method for selecting those needles which are to seize the yarn from the various feed stations to form knitwear.
2. Description of the Related Art
Circular knitting machines consist generally of one or two needle cylinders 1 which, as shown in FIG. 1, comprise tricks 2 in their outer cylindrical surface.
The tricks 2 represent the guide for the needles which during their vertical travel form the stitch loops in cooperation with the sinkers.
The number of tricks is equal to the number of needles which slide in them with reciprocating movement by the effect of raising and lowering cams not shown in the figure.
Generally, in hosiery machines the number of tricks and needles is between 200 and 400.
The cylinder is rotated and with it there rotate the needles which during their reciprocating movement are fed with yarn in fixed angular positions when in their highest point of travel by feed stations consisting of one or more yarn guides which are selectively presented to the needle hooks so that they seize from them the yarn with which they have to produce that determined portion of knitwork.
To produce hosiery articles or other types of knitted hose, generally only a fraction of the available needles are used at the same time and in the same manner, except for the plain knitwork parts of the hose, for which all the needles are operated between their maximum and minimum level, all being fed with yarn at each knitting course, and all being moved in the same manner.
When the machine is not producing plain knitwork, in order to produce other types of knitwork some needles are required to produce stitch loops and therefore be raised to the maximum level at the feed station in order to seize the yarn, while others have to be raised to an intermediate level to take up yarn without clearing the previous stitch in order to form a tuck stitch, or have to be raised with a certain delay so that they do not seize the yarn fed in that feed station and therefore do not form new loops with it. In other words a needle selection has to be made. This means that before each feed it has to be determined which and how many needles must undergo a certain travel and which and how many other needles must undergo a certain different travel or indeed undergo no travel.
Again with reference to FIG. 1, this selection is effected by the jacks 4 which slide in the same tricks 2 as the needles lying above them, to urge the needles 3 upwards and move them to a higher level in order to seize the yarn. After seizing the yarn the needles are controlled in their reciprocating movement by their own cams and counter-cams which are fixed relative to the cylinder, but are not indicated in the figures.
FIG. 1 shows an elastic jack 4, able to radially flex its lower end.
FIGS. 1 and 2 show a preferred embodiment for the needle cylinder 1, in which the tricks 2 are formed by inserting strip inserts 2' into the cylinder surface, this resulting in guide surfaces of greater accuracy and greater wear resistance. When the jacks 4 have moved their needle into its working position they withdraw from the needle butt and return downwards. If the needle, after completing its task of seizing the yarn and forming the stitch loop and therefore being at its minimum level, is not required to seize a further yarn from another feed it remains at this level because its control jack remains in its lower rest position.
The shank of the jack 4 comprises in its middle part a projection 5, i.e. the upper guide butt, which comes into engagement with its own control cam 6 for urging the jack downwards when it has completed its task of raising the needle 3, as far as an opposing cam 7.
Proceeding downwards along the jack shank there is a lower butt 8 which comes into engagement with the lower cam ring, consisting of a raising cam 9 which raises the jack together with its overlying needle, this therefore being selected to seize the yarn, and a cam 10 which with its inner face engages the vertical face of the butt 8 to urge the foot of the elastic jack 4 into the interior of the trick 2 by flexing it. When in this position of approach to the interior, the butt 8 is unable to engage the contour of the raising cam 9.
The lowering contours 6 and the raising and approach contours 9 and 10 are offset angularly and operate at different times on each jack.
In circular knitting machines, needle selection is generally conducted by maintaining those jacks corresponding to the needles to be raised by the butt 8 in a position displaced outwards to cause it to engage the raising contour 9, while maintaining those jacks corresponding to the needles not to be raised in their position of approach to the interior, whether elastic jacks or conventional rigid jacks are used.
When elastic jacks are used, as in the present invention, they tend spontaneously to move their butt 8 outwards to engage the contour 9 by virtue of their elastic force, whereas with conventional jacks their approach movement is effected by fixed cams arranged about the cylinder.
The elastic jacks are maintained in position so that the flexure of their lower part does not cause their upper part to escape from the trick, this being achieved for example by one or more rigid circular rings 11 fixed to the cylinder and surrounding their upper part. The purpose of these springs is to oppose the forces which flex the shank of the jack so that the forces acting on the butt 8 induce said flexure, rather than causing the upper part of the jacks to leave the tricks. A further rigid ring 12 limits the elastic return travel of the foot of the jack 4 to the distance sufficient for it to be able to rise on the contour 9 and not beyond.
As already stated, the purpose of the needle selection device and procedure is to exclude from this totality of jacks, by maintaining them in their inward position, the jacks which control those needles which in forming the particular stitch are not required to be raised.
The conventional selection system uses mechanical selectors acting on a series of intermediate butts, but this type of selection has considerable limits in terms both of operation and of the number of possible selections.
The most recent machines use electromagnetic selection devices which allow a greater selection speed and a greater number of programmable selections, with advantages in terms of machine production and the greater variety of possible patterns.
These selection devices are divided essentially into two categories, namely fixed devices which do not rotate with the cylinder and are positioned to precede each feed station, to which the jacks are presented in sequence as they rotate, and selection devices which rotate together with the cylinder (and with its jacks) and which are therefore always each in a position corresponding with its own jack and can thus act on the jacks at any moment, rather than only during the very short time in which the jack passes in front of them.
This second type of selection must also be effected after the jacks have returned downwards but before they encounter the raising cams 9, but there is greater freedom with regard to the requirements of synchronization and the constraints on the time available for the selection, compared with selectors of the first type.
Selection devices of the first type are described in European Patent No. 0 379 745 in the name of Furia, in European patent application 219029 in the name of Lonati, in GB patent application 2,008,157 in the name of Shima, in GB patent application 2,112,822 in the name of Elitex, in GB patent 1,436,607 in the name of Precision Fukuhara, and in French patent 1,564,603 in the name of Mayer, in which the jack selection is generally achieved--prior to each feed--by deforming or displacing auxiliary members arranged around the needle cylinder by means of fixed cams and then retaining or releasing these members by means of electromagnetic actuators.
Selection devices of the second type are described in European patent application Public. No. 0 379 234 in the name of Gargiani and No. 0 441 005 in the name of SAVIO.
The present invention relates to a device and method of the first aforesaid type for needle selection in a circular knitting machine and is described hereinafter with reference to FIGS. 1 to 5, which show typical embodiments thereof by way of non-limiting example.